Vulcanization accelerator



Patented July 20, 1948 VULCANIZATION ACCELERATOR Edward Carr and George "E. P2 Smith, Jr.,-

Akron, Ohio, assignors to The Firestone Tire & Rubber Company, Akron, Ohio, a corporationof ()hiow No Drawing. Application May 26, 1943,

Serial No. 488,555

12 Claims; 1

Thi'sinvention relates to thevulcanization of rubber; and relates especially to a new class-of chemical compounds which are valuable accelerators of the vulcanization of rubber" or rubberlike substances:

It is a primary object of the present invention to provide a new class of chemical compounds.

Another tobject-is to provide" a new class of improved rubber: vulcanization accelerators of the delayed action', non-scorching type.

Another object is to provide a method of vulcanizing rubber; whereby scorching or pre-vulcanization during processing of the rubber com pound is'preventedgbut extremely rapid vulcanization is obtained atcustomary vulcanizing temperatures.

Another object compositions possessing the ability to vulcanize extremely rapidly at ordinary" vulcanizing tem peratures, but? free'fromany tendency to set-up or pre vulc'anize' atv rubber processing temperatures.

A further object is to provide vulcanized rubber of improved quality,= possessing the characteristics of high-"modulus" and tensile;-low"hyster=" esis and a high inherent resistanceto' deteriorathetic-rubber; The new compounds may be con veniently'prepared byxidizing' a mixture of a non' arylene -2-mercaptothiazoleand ammonia or a. primary amine; Thepreparative oxidationreaction may be eiiected by treatinga mixture of the-:mercaptothiazole and an excess of the amine iniian alkaline aqueous medium with-one of the following oxidizing agents: chlorine, bromine,

iodine, hypochlorous acid; 'hypobromous acid,

hypoiodous'acid, and alkalimetal and alkaline earth metal salts of said acids. The oxidation reaction is believed-to comprise the'direct action of the oxidizing agentomamixtureiof the mercaptothiazole andone equivalent of the amine. The desired substances produced by this oxidation reaction are organic compounds containing nitrogen andsulfur.

Thei'new class of chemical compounds is--be-- lieved to possess the following-type iormulaz R1-C-N o-s'- N-R3 is to provide: improved rubber A solution consisting-of 500 .mL- Of-BthEI and: 100;- grams of gch'loro -acetone was poured on tor 119 grams" of ammonium dithiocarbamate (pre c pared from ammonia and carbon disulfideh in a Z-liter Erlenmeyer flask. The resulting mixture consisted" of two phases, the ether solution '01" chloro acetone and the solid phase of ammonium dithiocarbamaten In the course 'of -15 minutes theaether b'eganzt'o boil. The reaction was vigorous for an hour and then subsided. The mixture was=al1owedto stand at room temperature for several hoursfiand then was filtered. The filtla-tfi' alight yellow ether Samoan, was evaporated-ion a stem bath to leave: a residue of a dark brown liquid which solidified upon cooling. The solid residue was leached with dilute sodium hydrox'i e solutior'rgand the 'leachi-ngs were then acidifi' d with -hydrochloric'=acidto precipitate a crea' colored crystalline -solid melting" at I 85 -875 This solid, -z -merca'pto 4e-methylthiazoleigwas ob tained in' ayield of- 78 grams 1 An' aqueous solution was 1 prepared containing 3'l g'rams *of the 'mercaptothiazoley 82 gramscycio hex-ylamine and-"lograms of sodium: hy droxid'e' in a-volume of-"800 1111a An aqueou's iodiriew solution; containing =grams of iodine and 60 grams of potassium iodide in a vo1ume of 650 ml ipwas graduallyadded to the solution of the-' thia'zo1e and -amine,-with stirring f over a periocl of two hours, the reactionsolution being- -main 'tained at a temperature of 8-10 C. The solid product which precipitated"'from the reaction mixture was separated-and. dried This product, N-c-yclohexyl 4. (4-'methy1-2-thiazyl)= sulfenamiderwas-obtained as 40 gramscf cream colored 'cryss talsimelting at-5051 Ci This sulfenamide de rivative possesses-the following: formula:

The 'sulfenamide was tested as a rubber vul- 'canization accelerator by comparing it with the standard accelerators, mercaptobenzo-thiazole and dibenzothiazyl disulfide, the latter being a delayed-action accelerator, in the following rubber formula:

Ingredients 23 232 2? fiubbr (Smoked Sheets) 100.00 Sultan, 3.00 zinc oxide 5. Steanc acid. 1.10 Accelerator i 0. 75

Samples of the three rubber compositions, so

formulated, were heated for 30 minutes at 240 -F. to determine whether or not they possessed any tendency to pre-vulcanize or set-up during processing operations prior to the usual vulcanizing step, and the following physical testing data were obtained:

Modulus of Elasticity $55 Accelerator in lbs./in 2 in lbsjinfl at elobgoaytolon at break Mercaptobenzothiazole 375 2175. Dlbenzothiazyl disulfide No cure. No cure. N cyclohexyl (4-methyl-2- iazyl) sulfenamide .do Do.

Other samples of the same rubber compositions were heated for minutes at 280 F. to determine the relative accelerating properties of the respective accelerators, and the following data were obtained:

Modulus of Elasticity ff ii Accelerator tin1lbs./i? in lbs /in 2 a e onga ion of 600% at break Mercaptobenzothiazole 650' 2, 550 Dibenzothiazyl disulfide 525 2, 450 N-Cyclohexyl (4-metliy1-2-thiazyl) sulfenarnide 1, 675 3, 775

Earample 2 Ammonium dithiocarbamate was condensed with3-chloro-2-butanone (B. P. 113-116" C., separated by distillation from a commercial sample of chlorinated "methyl, ethyl ketone) to produce 2-mercapto 4,5 dimethylthiazole (light yellow crystals, melting at 162-163 C'.) in a manner similar to the preparation of 2-mercapto-4-methylthiazole from chloro-acetone, described in Example 1. An aqueous solution comprising four moles of cyclohexylamine, one mole of the fi-mereapto- 4,5dimethylthiazole and two moles of sodium hydroxide was oxidized at 8-10 C. by an iodinepotassium iodide solution to produce a 93 per cent yield (based upon the thiazole) of N-cyclohexyl (4,5-dimethyl-2-thiazyl) sulfenamide, having the following formula:

The above sulfenamide Was obtained as white, glistening, crystalline leaflets, melting at 92-94 C.

In a similar manner, a solution of ten moles of isopropylamine, one mole of 2-Inercapto4,5-dimethylthiazole and two moles of sodium hydroxide was oxidized by iodine to produce a yield of per cent of N-isopropyl (4,5-dimethyl-2-thiazyl) sulfenamide, having the following formula:

The isopropyl derivative was obtained as a white, crystalline solid, melting at 62-63 C.

The above two derivatives of 4,5-dimethyl-2- thiazylsulfenamide were tested as vulcanization accelerators in the rubber formula set out in Example 1. No vulcanization resulted on heating the compositions containing the sulfenamide derivatives for 30 minutes at240 E. On heating the rubber compositions for 20 and 40 minutes at 280 F. the following data were obtained:

z igg figfigi' Tensile Strength at elongation of g at Accelerator 600% re 20 min. 40 min. 20 min. 40 min.

. N-Cyclohexyl(4,5-din1ethyl- Z-thmzyl) sulfenaznlde 1,650 2,775 3, 475 3,725 N-Isopropyl (4,5-dunethyl- I 2-thiazyl) suli'enamide 1,475 2,600 3,150 3,700

Example 3 Ammonium dithiocarbamate was condensed with 1-chlor0-2-butanone (B. P. 134-136 C., separated by distillation from a commercial sample of chlorinated methyl, ethyl ketone) to produce 2mercapto-4-ethylthiazole (yellow solid melting at 80-85 C.) A cold aqueous solution containing one mole of the thiazole, three moles of cyclohexylamine and two moles of sodium hydroxide was oxidized by iodine to form a 77 per cent yield of N-cyclohexyl (4-ethyl-2-thiazyl) sulfenamide having the foil-owing formula:

This sul-fenamide derivative was obtained as a soft, tan-colored solid, melting at 65-68 C. The new compound was tested as a vulcanization accelerator in the rubber formula set out in Example 1. No vulcanization occurred on heating the composition for 60 or 80 minutes at 240 F., indicating that the compound is an extremely safe delayed-action accelerator. When the compowasitiom wasrheatedieozandrfiovminutes :aflQSO". the

aresulti ng data's were dob'tained *A conrmercial*mixture of 1-chl-oro- 2-butanone and 3-chloro-2-butanone (approximately one -part to three-- parts, respectively produced by *chl'orinatingmethyl; ethylketonel was condensed with a'mmonium dithiocarbamate to form asolid mixture 'of 2 niercapto l-ethylthiazole' and 2- mercapto-4,5-dimethylthiazole. An aqueous solut-i'on" containing 145"grarns-of the mixed thimolest-90 per cent pure); 80 grams rofsodiumhydioxide and" 250gran1s"ofcyclol'iexylamine' in a volume of five liters Was cooled-in an ice bath and oxidized by aamixture'of chlorine gas and air; passed into the: agitated solution during the course of three hours. The product, a mixture 1 or about; one part of N cyclohexyl l-ethyl-Z thi- "azyl y sulfenami'de and three-parts ofN-cyclohexyl (4;5 dimetliyl-2 thiazyl)-= =sulfenarnide, precipn it'ated'as a soft;tan solid, in a yield' of-l'65 grams (78 per cent)melting at about 57-'7'7"'C. -The mixture of 'sulienarnideswas tested in the standare aceeler-ator test formulaslrowm in Example 1. No vulcanization occurred on heating the rubber composition .for- 60minutes at 240 F. On

' acted with 2-mercaptd-4,5 dirnethylthiazole1'by oxidation of an: alkaline aqueous. mixture of one I mole iof'the thiazole and fivemoles -of the amine by means of an. aqueous 'iodine potassiurniiddide solution. The 'iormulasof the specific/sulf'enthiazole to produce N-sec. amyl (4-iethyl-2- thiazyl) sulfenamide or N-methyl-n-propylcarbin (4-ethyl-2-thiazyl) sulienamide havingnthe follow-ingaformula:

heating the rubber composition for 20 and 60 min- H5OT'G' N utes at 280 F., the following data were obtained: '/C'-SNCH'CH'CHg-C'Ha M d HCS .Hv H3 o ulus oLElasi tic ty sl ,Tggfiigfifit g The yields-and melt1ngrpo1nts .of ther-sulfenat elongiiwn Of break amide derivatives so produced are set out iincthe Accelerator 000 /0 1 followmgetable:

. 20 min. 60 min; =20 min. .60 min. i 1 v i r i 2-Thiazylsiilfenamide Yield 'Meltimreoinr Mixture of N -cyclohexyl(4-- ethyl -2-thiazyl) sulfen- N-Sec.butyl-4,5-dimethyl- 72''51'52IC'. amide and N-cyclqhexyl N-Sec.amy1-4,5-dimetl1yl- 56- 40:42".C. (4,5d1methyl-2-th1azyl) N-Sec.hexy1-'4, fi dimethyl 51 i (Liquid)? sulfenamlde "L. 1,725 2,67 3,350 3,225 i"N-Sec&1amy1-4-'ethyl- ':(Li'qui l).i

Example .5 Eachof the fourabove sulfenamidederivatives Fi-fty ml. lof' 5.5: per cent sodium hypochl'ori te msoluti-oni were added to 100 mlu of concentrated 'ammoniacontaining 25 grams of cracked 'ice- 1 To the resulting solution" there was gradually added,"

with stirring, 10.5" grams or 2-mercapto-4,5di methyl-thiazole dissolved in a solution of 5.52 grams of sodium hydroxide in 100 ml. of water.

After the addition 'ofa portion of the thiazole, solutiona flocculant precipitate appeared which" soon became very bulky in the reaction vessel. The mixture was stirred for a short time after the addition"of'theentire quantity of the thiazole solution. Then the white,"crysta1line precipitate wasiseparated, washed withewater' and dried; The p'roducta4,5-dimethyl-thiazylsulfenamide,

H30;CN

C-S-NH:

H3oos is an effective rubber vulcanization accelerator of the delayed-action type, being similar in accelerating activity to the alkyl and cyclo-alkyl derivatives specifically described above.

wasitested in the rubber accelerator test formula of 'Ex ample 1, and were found to cause no v ulcanization of the rubber when the latter-was utes at 280-F.', the following data were obtained:

Modulus of Elasticity in lbs/in] i ffligi il atelongation of r a Accelerator 600 1e 40 min. min. 40 min. '60 min.

"N-Sec butyl'(4,5-dirnethyl- 2-th1azyl) sulfenarnide 2,450 2, 425 3,350 3, 575 N-Sec.- amyl (4,5-zl11nethyl- -2-thi'azyl) su-lienamlde 2,575 2,550 3,775 3, 625 'N Sec. hexyl (4,5-dimethyl- Z-thiazyl) sulfenamide 2,450 2, 450 3, 525 3, 525 N-Sec'. amyl ='(4 ethy1 2-th1- azyl) sulfenamide 2,750 2,600 3,800" I 3,325

The various members of the new class of chemical compounds are equally effective delayed-action vulcanization accelerators in rubber tread compounds, latex compounds or other conventional types of vulcanizable compounds of rubber, reclaimed rubber, or synthetic rubber, and consistently produce rapid-curing compositions, which in the vulcanized'state possess unusually high modulus, tensile and abrasion-resisting properties. The various synthetic rubbers vulcanizable by heating with sulfur are herein considered equivalent to rubber, examples .being butadiene polymers, isoprene polymers and various interpolymers of conjugated diolefins and vinyl compounds, such as Buna S (copolymer of butadiene and styrene) and Buna N (copolymer of butadiene and acrylonitrile). Although sulfur has hereinabove been mentioned as the preferred vulcanizing agent, other known vulcanizing agents susceptible to acceleration are contemplated.

The preferred class of sulfenamide derivatives may be prepared by other methods than those mentioned above. For example, a mixture of a non-aromatic mercaptothiazole and ammonia or a primary amine may be oxidized by hydrogen peroxide or other oxidizing agent. The invention is not limited to derivatives prepared in accordance with any particular method, but includes the preferred class of compounds, however they may have been formed.

In addition to the above-enumerated desirable properties imparted by the new accelerators to rubber compositions, it has been found that the vulcanized compositions also are highly efiicient, having low hysteresis characteristics. When compared to conventionally accelerated vulcanized rubber compositions, the new compositions are found to be unusually resistant to deterioration upon flexing or aging.

Conventional accelerator activators may be employed to an advantage with the new class of accelerators when extremely rapid vulcanization is desired, especially at lower temperatures. Also, the new accelerators may be used in combination with other accelerators, such as a guanidine (e. g., diphenyl guanidine) or a conventional mercaptothiazole derivative (e. g., mercaptobenzothiazole or dibenzothiazyl disulfide), in order to produce rubber compositions having especially rapid or specific vulcanizing properties. The new accelerators may be employed in other proportions than the proportion shown, but will normally be utilized in the range of 0.1 to 10 parts per 100 parts of rubber.

Modification may be resorted to and obvious chemical equivalents substituted in the specific examples of the invention without departing from the spirit or scope of the invention as defined in the appended claims.

What is claimed is:

1. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of N-cyclohexyl 4-methyl-2-thiazyl) sulfenamide.

2. A vulcanizable rubber composition including sulfur and N-cyclohexyl (4-methyl-2-thiazyl) sulfenamide.

3. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of N- cyclohexyl (4-methyl-2-thiazyl) sulfenamide.

4. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of N-isopropyl (4,5-dimethyl-2-thiazyl) sulfenamide.

8 5. A vulcaniz'able rubbercompo'siticn including sulfur and N-isopropyl (4,5-dimethyl-2-thiazyl) sulfenamide.

6. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of N- isopropyl (4,5-dimethyl-2-thiazy1) sulfenamide.

7. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of N-cyclohexyl (4-ethyl-2-thiazyl) sulfenamide and N-cy-clohexyl (4,5-dimethyl-2-thiazy1) sulfenamide.

8. A vulcanizable rubber composition including sulfur, N-cyclohexyl (4-ethyl-2-thiazyl) sulfenamide and N-cyclohexyl (4,5-dimethyl-2-thiazyl) sulfenamide.

9. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of N- cyclohexyl (4-ethyl-2-thiazyl) sulfenamide and N-cyclohexyl (4,5-dimethyl-2-thiazyl) sulfenamide.

10. The method of vulcanizing rubber which includes heating rubber and sulfur in the presence of a substance having the formula m-o-N C-S-N-Ra arc-s wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl radicals at least one of said R1 and R2 being an alkyl radical, and R3 is one of the group consisting of hydrogen, alkyl radicals and cyclo-alkyl radicals.

11. A vulcanizable rubber composition including sulfur and a substance having the formula wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl radicals, at least one of said R1 and R2 being an alkyl radical, and R3 is one of the group consisting of hydrogen, ,alkyl radicals and cyclo-alkyl radicals.

12. A vulcanized rubber product prepared by heating rubber and sulfur in the presence of a substance having the formula m-o-N wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl radicals at least one of said R1 and R2 being an alkyl radical, and R3 is one of the group consisting of hydrogen, alkyl radicals and cycio-alkyl radicals.

EDWARD L. CARR.

GEORGE E. P, SMITH, JR.

REFERENCES CITED The following references are of record file of this'patent:

UNITED STATES PATENTS in the Certificate of Correction PatentIN 0.:2,445,7 22. July 20, 1948.

EDWARD L. CARR ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 29, for the words stem bath read steam bath; column 4, line 10, for that portion of the formula. reading N read N-CI and that the said Letters Patent should be read with these corrections therein that r the same may-conform to the record of the case in the Patent Office.

Signed and sealed this 14th day of December, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

